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Removes Carbon Dioxide From The Blood

by Lyndon Langley
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Removes Carbon Dioxide From The Blood

Removes Carbon Dioxide From The Blood

Carbon dioxide (CO2) is a colorless, odorless gas that makes up approximately 0.04 percent of our atmosphere and plays an important role in regulating body temperature as well as other metabolic processes like respiration. Although it’s not toxic at low levels, high concentrations can cause nausea, vomiting, headaches, weakness, dizziness, disorientation, confusion, irritability, and unconsciousness among others symptoms. In fact, CO2 has been used on battlefields to incapacitate enemy combatants by inducing loss of consciousness. And when inhaled, it can also lead to death due to suffocation or cardiac arrest.
Because of its potential harm, it’s imperative for all animals — including humans — to remove excess amounts of this gas from their bodies through breathing and circulation. This process is carried out by the lungs and kidneys using special cells called hemoglobin-containing red blood cells (RBCs). Hemoglobin molecules inside these RBCs bind with oxygen (O2) while freeing carbon dioxide (CO2), which is then expelled from your body via urine.
But how exactly does this whole thing work? Let’s start with what happens during normal breathing. When you breathe air, some of it enters your lungs where it’s absorbed into the bloodstream. Once there, most of it dissolves into water molecules so that they can be transported throughout your body while the rest gets metabolized. But unbeknownst to us, small amounts of CO2 are released from the lungs along with oxygen (O2) every time we take a breath. However, because oxygen is heavier than carbon dioxide, they tend to stay together within our bloodstream. Hence, the amount of CO2 present in our blood is equal to the amount of O2 available. So if you inhale pure oxygen (which contains only one atom of O2 per molecule), the remaining CO2 will get depleted immediately.
In contrast, when we exhale, the reverse happens; oxygen from the lungs mixes with carbon dioxide in the bloodstream. During exhalation, the partial pressure of carbon dioxide in the alveoli is lower than atmospheric level, resulting in less CO2 being dissolved into water and more of them getting removed from the bloodstream. Therefore, the overall concentration of carbon dioxide in the blood decreases over time. This process helps regulate the pH balance of our blood, which ultimately maintains normal body functions.
Now let’s talk about how the kidneys play a crucial part in filtering carbon dioxide from the blood stream. To do that, we first need to understand how kidneys filter waste products out of the blood. They accomplish this task by secreting tiny filtration structures known as nephrons. These specialized units consist of thin branches known as glomeruli, loops known as proximal tubules, and distal tubules filled with fluid. At the beginning of each loop, a kidney bean-shaped structure known as Bowman’s capsule separates the glomerulus from the rest of the renal tissue. Glomerular capillaries then branch off from the ends of the loops, creating connections between the tubules and the outside environment. Here, plasma flows into the glomeruli, and since the vessels are too narrow, large protein complexes called albumin and immunoglobulin G (IgG) are stuck here.
Once inside the glomeruli, blood proteins undergo several changes. First, IgG binds to antigenic substances in the blood plasma and prevents them from passing through the walls of the capillary. Next, albumin absorbs sodium ions (Na+) and chlorine (Cl-) ions from the blood plasma. Finally, the filtered serum containing wastes such as nitrogenous compounds, urea, uric acid, creatinine, etc., is released back into the body. Now that we know what goes on in the kidneys, let’s find out how they filter CO2 from the blood.
It starts with the formation of brush border membranes around the outer side of the nephron loops. Within these borders lie microvilli projecting into the lumen of the loops and covered with enzymes that help break down the carbon dioxide. After absorbing O2 from the plasma, these enzymes convert CO2 and hydrogen ion (H+)-rich water inside the loops into bicarbonate (HCO3-) and hydroxyl ions (OH-). Then, HCO3- is secreted into the interstitial space and neutralizes Na+, Cl-, Ca2+ and Mg2+. Since the flow rate of the plasma is much higher than the rate of secretion, additional HCO3- must be continuously produced to maintain equilibrium. As a result, carbon dioxide becomes attached to HCO3- via strong chemical bonds instead of free floating around in solution.
After that, the newly formed bicarbonate diffuses across the apical membrane of the epithelial cells that line the surface of the loop. It eventually reaches the basolateral membrane where it combines with the H+ ions to form yet another compound called protons (H+). Protons then combine with Na+ ions to produce new particles called sodium cations (Na+). The now-ionized Na+ ions pass through channels embedded in the cell wall and move towards the inner side of the loop, where they contact reabsorption sites loaded with calcium ions (Ca2+). Once this occurs, the newly created calcium cations (Ca++) combine with chloride ions (Cl-) to form new particles called calcium chloride (CaCl). Eventually, CaCl passes through channels located on the opposite side of the loop where it comes in contact with magnesium ions (Mg2+). Since Mg2+ is bigger than CaCl, it blocks its passage and keeps the calcium cations away from the absorption site.
At last, the calcium cations dissolve into the fluid contained in the distal tubule. This process removes the carbon dioxide from the blood, but unfortunately, it also deprives the kidneys of needed calcium. To compensate for this, two hormones called calcitriol and parathyroid hormone stimulate bone metabolism and release calcium into the blood. Calcitriol increases the number of receptors for vitamin D3, which allows it to boost the efficiency of calcium absorption by kidneys. Parathyroid hormone stimulates production of osteoclasts, which increase the rate of bone resorption. Thus, the bones become rich in calcium and phosphorus, which later deposits in the kidneys’ calyxes. However, due to the lack of sufficient calcium, the mineralization process takes longer and results in less efficient filtering activity.
So far, we’ve learned how the kidneys eliminate carbon dioxide from the blood. Next, let’s discuss how lungs function in the same regard.
Lungs have a similar structure to kidneys, except that they’re encased in a rib cage. Also, unlike kidneys, lungs don’t contain any type of internal organs. Instead, they have a network of capillaries permeating through millions of tiny sacs that fill up with air. Each lung consists of three lobes separated by bronchial tubes lined with mucus membranes made up of cilia. Surrounded by surfactants, cilia keep the lungs moist and clean. Cilia extend from the tips of the cilia, forming a tuft-like layer surrounding the alveolar ducts. This tuft protects the lungs from foreign substances and allows healthy gases to enter the lungs.
When we inhale air, it enters the trachea and fills both lungs. Upon inhalation, oxygen-enriched air moves toward the center of the right lung through a series of branching passages called pulmonary arteries. These arteries end at clusters of microscopic bubbles called alveoli. Inside the alveoli are millions of thin-walled sacs called alveoli that fill with air. Alveolar walls are composed of type I pneumocytes whose surfaces are covered with microvilli. Type II pneumocytes make up 90 percent of the total population of pneumocytes in the lungs. Their flat surfaces come in direct contact with the alveolar walls, allowing them to exchange materials directly with the bloodstream.
During exhalation, carbon dioxide, water vapor, and sometimes nitric oxide leave the lungs through the pulmonary veins. Before departing, however, CO2 attaches itself to albumin molecules produced by type II pneumocytes. While moving through the capillaries, albumins are broken down into smaller pieces called globulins by endothelial cells lining the walls of the capillaries. Once the carbon dioxide attaches to albumin, it leaves the lungs together with the globulins. Because globulins are lighter than CO2, they float freely in the bloodstream until they reach the liver. There, globulins are converted back into albumins and sent to various tissues in the body.
So far, we’ve discussed how lungs work to remove carbon dioxide from the blood. What about sweat glands? Sweat glands produce sweat that evaporates once the skin heats up. Due to this property, sweat carries with it salt and water molecules. Just like our lungs, sweat glands also have pores that allow sweat to exit the skin. Like the respiratory system, the excretory system is also tasked with eliminating waste products from the blood.

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1 comment

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